TF-HC-3F

This tube was designed by H. J. Round and made by Ediswan for use by the Marconi Wireless Telegraph Co Ltd (GB). The tube had three filaments. These were mostly lime coated platinum wire, with a provision to use them singly if required. Some tubes had 4 base contacts in the base sheathing. Bases were usually nickel plated brass. Properly used, these tubes achieved amazing sensitivity and performance.

Some of these valves had a tubulation at the top which contained amalgam instead of the usual asbestos. This tubulation contained a means for adjusting the vacuum.